In association with the progress of digital printing, attention has been paid to variable data printing as a form using its feature. A print form in which a part of printed matter is changed as variable data every copy or the like makes the most of characteristics of a digital printer such as an electrophotograph or the like. In the early variable data printing, a variety of VDP (Variable Data Printing) languages have been used in many companies so far. However, nowadays, a PPML (Personalized Print Markup Language) as a standard language is defined and widely used. In the PPML, as elements adapted to draw a page, there are two elements of a reusable object which is repetitively referred to and a local object which is referred to only once. The reusable object is used in the case where a single drawing object is arranged at a plurality of positions in a page, between pages, or between jobs. Ordinarily, a drawing object such as local object, reusable object, or the like uses PostScript (registered trademark; hereinbelow, abbreviated to PS) or a PDF as source drawing data. Those source drawing data is converted into a raster image through an RIP process and, thereafter, arranged on the page. In the case where it is clear that the data is reused like a reusable object of the PPML, an image processing apparatus caches a raster image obtained as a result of execution of an RIP process from the source drawing data. Thus, a very high speed drawing process can be performed. However, in the case where the raster image is color data of high resolution and high gradation, its size is very large. Therefore, a memory of a large capacity is necessary for the image processing apparatus. To solve such a problem, there is also a method whereby intermediate data before the data is converted into the raster image is formed from the source drawing data and cached into the image processing apparatus. Although a time necessary to render the intermediate data remains, a memory capacity necessary to cache can be remarkably reduced and such a method can be regarded as a compromise plan which takes a balance between the memory capacity and performance into consideration.
Further, a standardization of PDF/VT (Variable data and Transactional) has been performed as a VDP language of the next generation. The PDF/VT is a format based on the PDF and it is expected to use the PDF with respect to the specifications of the page drawing. In the PDF/VT, reuse of the drawing object is instructed by using XObject as a drawing component of the PDF. The image processing apparatus can execute the high speed process by caching the reuse-designated XObject by some format. Since the PDF/VT is based on the PDF, an affinity with the PDF workflow or utility existing hitherto is very high. A tool such as existing previewer, preflight check, page layout application, or the like which can process the PDF can be used without a large change. It is an advantage which is not obtained in the VDP language such as a PPML in the related art, and a future spread of such a tool is expected.
If the PDF/VT has been spread as a standard language of the VDP, the occurrence of a demand for conversion from the VDP language in the related art such as a PPML or the like into the PDF/VT is forecasted. By converting into the PDF/VT, the existing VDP data can be used as a resource. It is also because even in the case where the existing VDP language is used, it can be integrated with the workflow based on the PDF. Such a converter for converting from the PPML into the PDF exists (for example, refer to Patent Document 1 (specification of U.S. Patent Application Laid-Open No. 2005-125724)).
In the PPML, a layout description is defined and a print data format such as PS, PDF, or the like is used as a drawing object. Also in the case of converting from the PPML into the PDF/VT, it is necessary to convert the print data for those drawing objects into the PDF. As a processing method of the PS data, two kinds of methods using the existing processing system are considered. One is a method of replacing a description of the PS to a description of the PDF. Drawing models of the PS and the PDF are very analogous and a grain size and an abstract degree of the drawing are maintained almost as they are. The other is a method whereby image data is formed by the RIP which interprets the PS and a PDF comprising the image data is formed.
However, according to the method of replacing the description of the PS to the description of the corresponding PDF, a total converting efficiency of the conversion from the PPML into the PDF/VT and, further, into the raster image is low. Since the format is converted while an information amount of the draw command and the drawing color is simply held, according to the conversion of such a level, the obtained image is not close to the raster image. Therefore, a long time is required for the RIP process of the PDF/VT after the conversion. Even in the case of the VDP language, a possibility of the occurrence of a case where the RIP process is not in time for an engine speed is high. According to the conversion into the image by the RIP, on the other hand, although the total converting efficiency is high, there is such a problem that a data size is very large. If all of the image data is converted into images, since the RIP process becomes unnecessary, there is a surplus processing time of a controller CPU for RIP upon printing. Consequently, it takes a time for conversion from the PPML into the PDF/VT.